In zero gravity, a candle’s flame is round and blue
On Earth, when the candle burns the heated gases rise upward pushing combustion products along with them while drawing fresh air with oxygen towards the flame. This process is called convection, hot air becomes light and goes up, while the cool air stays heavier and comes down. But it doesn’t occur in space. Instead, the combustion products accumulate around the flame causing it to be cut off from oxygen and eventually going out. Though the candle does get oxygen through diffusion, the process is a 100 times slower than it is on Earth.